An electromagnetic actuator for driving a hydraulic control valve, which is provided in a rotational center of a valve timing control device for an internal combustion engine, is known in the art.
In a prior art, for example, disclosed in German Patent Publication DE 10 2010 060 180 A1, an electromagnetic actuator is provided at a position opposing to a hydraulic control valve and a rod connected to a movable core pushes a spool of the hydraulic control valve when electric power is supplied to an electromagnetic coil. On the other hand, when the electric power supply to the electromagnetic coil is cut off, the rod is returned to its initial position by a spring force of a spring provided in the hydraulic control valve.
In the electromagnetic actuator, an air breathing passage is formed in an outer wall of the hydraulic control valve so as to communicate a movable-core chamber (in which a movable core is accommodated) to the atmosphere. Since air passes through the air breathing passage, the air in the movable-core chamber does not prevent a smooth movement of the movable core.
In the hydraulic control valve driven by the electromagnetic actuator of the above prior art, an oil-discharge port is formed on a side to the electromagnetic actuator. According to such a structure, a structure for hydraulic passages of the hydraulic control valve is simplified and pressure loss of the oil flowing through the hydraulic passages can be decreased in order to enhance response of the hydraulic control valve.
On the other hand, the electromagnetic actuator of the above prior art has an air breathing passage at such an area, to which the oil discharged from the oil-discharge port of the hydraulic control valve is directly poured. Therefore, it may become a problem that the oil from the oil-discharge port and/or extraneous material contained in the oil directly flows into the movable-core chamber through the air breathing passage.
In such a case, namely, when the high-pressure oil injected from the oil-discharge port rushes into the movable-core chamber through the air breathing passage, the movable core is pushed by such rushed-in oil in a direction opposite to the hydraulic control valve. As a result, it may become difficult for a rod fixed to the movable core to keep its force for pushing the hydraulic control valve.
In addition, when temperature becomes lower, viscosity of the oil from the oil-discharge port becomes higher. When the oil of a grease-like condition flows into the movable-core chamber through the air breathing passage, sliding resistance between the movable core and an inner wall of the movable-core chamber becomes larger. Furthermore, when an amount of the oil flowing into the movable-core chamber is increased, and when an amount of the extraneous material contained in the oil and flowing into the movable-core chamber is correspondingly increased, it may become a problem that a sliding movement of the movable core is adversely affected by such oil and/or the extraneous material.